R. I. Tomov

University of Cambridge, Cambridge, England, United Kingdom

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Publications (36)68.41 Total impact

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    ABSTRACT: Porous metal supports for SOFC applications were produced via conventional powder metallurgy routes—tape casting and high-pressure injection moulding. The supports were sintered in vacuum at different vacuum levels and temperatures. Commercially accessible low-cost stainless steel 430L powder was chosen as source material. The relations between the vacuum sintering temperature and the supports properties were studied. The density and the open porosity distribution of sintered supports were determined by Archimedes' method, Optical Image Analysis and Hg-porosimetry. The microstructure and the stainless steel grain surface composition evolution were investigated by scanning electron microscope and energy dispersive X-ray spectrometry. direct ceramic inkjet printing (DCIJP) was employed as coating technology for depositing anode (NiO/GDC) and electrolyte GDC coatings. Suspension anode and electrolyte inks were developed in-house and the printing procedure was optimized to produce uniform coatings with thicknesses below 15 lm. The analyses confirmed that the as-produced substrates were suitable to support DCIJP deposited SOFC functional coatings.
    08/2015; 4(3). DOI:10.1007/s40243-015-0056-7
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    ABSTRACT: An entire cycle for fabricating a metal supported cell is developed, using porous SS430L as anode substrate, NiO-GDC as the anode, GDC as electrolyte and LSCF as cathode, as follows: (i) Tape Casting of porous SS430L substrate layers, followed by vacuum sintering (1100 o C); (ii) Brush painting of anode (NiO + GDC) layers, followed by a high heat flux treatment to induce rapid sintering; (iii) Plasma Spray (powder) deposition of GDC electrolyte layer leading to sintering; (iv) Ink-Jet printing of GDC colloidal suspension to give better finish to the 'rough' electrolyte surface, followed by high heat flux treatment; and (v) Brush painting of cathode (LSCF) layers on the electrolyte surface followed by high heat flux treatment. The cells are characterized for their microstructure and have shown highly dense electrolytes, and fine microstructures for anodes and cathodes. Process refinements are underway (with electrochemical characterization) to enhance cell performance and stack assembly.
    ECS Transactions 08/2015; 68(1). DOI:10.1149/06801.2245ecst
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    ABSTRACT: Direct Ceramic Inkjet Printing (DCIJP) was applied for fabrication of functional coatings in metal-supported SOFCs. An optimization procedure of the ink formulations and the printing parameters was performed allowing routine production of coatings with thicknesses below 20 µm with an additional benefit of surface defects planarization. Commercial low-cost stainless steel 430L powders were chosen as source materials. The supports sintering procedures was performed in vacuum. The density and open porosity distribution of as-sintered supports were determined by Archimedes' method and optical image analysis. The relation between the sintering conditions and the micro-structural characteristics of the metal supports and the coatings were studied. The influence of the printing parameters on the droplets spreading behaviour was explored. The microstructure and elemental distribution were investigated by Scanning Electron Microscope and energy dispersive X-ray spectrometry system. The analyses confirmed that DCIJP can be successfully applied for the production and modification of metal supported SOFCs.
    ECS Transactions 08/2015; 68(1). DOI:10.1149/06801.2491ecst
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    ABSTRACT: The industrial sector of flexible printed electronics has shown a dynamic growth in the last decades. Therefore, demand for new inks, coatings and printing methods leading to improved performances of the electronic components at room temperature is also increasing. Here, we present a study on the conductive properties of silver layers obtained by different coating and printing methods. The results obtained proved that drop-on-demand inkjet printing of water-based inks containing micron-sized silver flakes with narrow-size distribution is a feasible method for in situ fabrication of conductive silver coatings that does not require additional heat treatment. A rigorous optimization Taguchi experiment was carried out considering the major process parameters. This experiment showed that the printing pressure was the dominant factor defining the quality of the printed coatings and tracks.
    Journal of Electronic Materials 01/2015; 44(1). DOI:10.1007/s11664-014-3434-5 · 1.68 Impact Factor
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    ABSTRACT: The feasibility of inkjet printing of electrodes for direct carbon solid oxide fuel cells (DC-SOFC) was tested. A variety of materials was deposited by direct ceramic inkjet printing (DCIJP). The technology allows for easy modification of the coatings, including thickness control, porosity graduation and precise infiltration with catalytically active materials. The comparative tests showed a similar performance for screen printed and inkjet printed cells (peak power density of ca. 80 mW cm(-2) at 780 degrees C). In addition DCIJP offers minimization of the usage of expensive precursor materials. It was also found that infiltration of the anode by inkjet printing of sol inks (CuNiO3) can lead to an improvement in DC-SOFC performance.
    ECS Transactions 10/2013; 57(1):1359-1369. DOI:10.1149/05701.1359ecst
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    ABSTRACT: The direct carbon fuel cells with solid oxide electrolyte (DC-SOFC) and anodes deposited by inject printing (EM/DCIJP) were studied. The cells were fed with carbon fuel obtained by the direct RF plasma splitting of methane. Since the (EM/DCIJP)M/DCIJP technology allows easy modification of electrode material, the effect of Cu addition to the Ni–YSZ anode was investigated. The significant improvement of the cell performance with the new anode was observed.
    Electrochimica Acta 08/2013; 105:412–418. DOI:10.1016/j.electacta.2013.04.139 · 4.50 Impact Factor
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    ABSTRACT: h i g h l i g h t s Elementary reaction modeling and comprehensive experimental characterization. Coupling effects of carbon gasification and electrochemical oxidation process. Effects of carbon bed height, carbon conversion ratio, carbon utilization. a b s t r a c t A detailed mechanistic model for solid oxide electrolyte direct carbon fuel cell (SO-DCFC) is developed while considering the thermo-chemical and electrochemical elementary reactions in both the carbon bed and the SOFC, as well as the meso-scale transport processes within the carbon bed and the SOFC electrode porous structures. The model is validated using data from a fixed bed carbon gasification experiment and the SO-DCFC performance testing experiments carried out using different carrier gases and at various temperatures. The analyzes of the experimental and modeling results indicate the strong influence of the carrier gas on the cell performance. The coupling between carbon gasification and electrochemical oxidation on the SO-DCFC performance that results in an unusual transition zone in the cell polarization curve was predicted by the model, and analyzed in detail at the elementary reaction level. We conclude that the carbon bed physical properties such as the bed height, char conversion ratio and fuel utilization, as well as the temperature significantly limit the performance of the SO-DCFC. Ó 2013 Elsevier B.V. All rights reserved.
    Journal of Power Sources 05/2013; 243. DOI:10.1016/j.jpowsour.2013.05.149 · 6.22 Impact Factor
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    ABSTRACT: The objective of this study is to develop a cost-effective and environmentally friendly synthesis using soft chemistry based on Chemical Solution Deposition (CSD) using ink-jet printing for the deposition of ceramic thin films. The main advantages are the lower investment, the faster deposition with higher yield and the processing under ambient pressure enabling a complete continuous processing. The materials chosen for this study are TiO2 for development of photocatalytic layers; Yttria-stabilized zirconia (YSZ) is chosen as electrolyte material for Solid Oxide Fuel Cells (SOFC's) and for production of Thermal Barrier Coatings (TBC's); Lanthanum-Strontium-Manganese-Oxides (LSMO) magneto-resistive systems have been developed for obtaining functional magneto-resistive patterns.
    Nanoscience and Nanotechnology Letters 04/2013; 5(4-4):466-474. DOI:10.1166/nnl.2013.1563 · 1.44 Impact Factor
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    ABSTRACT: Development of direct carbon fuel cells opens new options for utlization of various carbonaceous fuels to produce electricity. Moreover, even some waste materials and by-products from industrial processes appear to be suitable for conversion in DCFC. An attractive opportunity is the use of carbon based by-products of methane plasma dissociation as a fuel. In this work comprehensive studies of two types of carbon fuels were performed, namely carbon powder (carbon A) produced by methane plasma dissociation and comercially available carbon black powder (carbon B). Before the electrochemical testing, both carbon fuels were characterized by X-ray, Raman, XPS/ESCA spectroscopy, thermal analysis (DTA, TG), electrical conductivity and other methods. Carbon A possessed larger particle surface area and lower ohmic resistance than carbon B, its purity was comparably high and ash content was low. Four different types of DCFCs were used during testing: all of them used solid electrolyte (8YSZ) and varied only anodic part of the cells. All the tests showed high degree of feasibility of the waste product of methane plasma splitting (carbon A) as a fuel for DCFC, very similar to the traditionally used as a reference carbon B.
    International journal of electrochemical science 08/2012; 7(8):6704-6721. · 1.96 Impact Factor
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    ABSTRACT: A detailed procedure for the preparation of gadolinium doped (10 mol%) cerium (IV) oxide (CGO) suspension for inkjet printing is described in this paper. The optimisation of inkjet printing parameters for the deposition of solid oxide fuel cell electrolytes was also performed using a custom-built drop visualisation system. Additionally, the uniformity of the deposited drop relics on porous substrates was evaluated. The ink used in this study was an evaporative type comprising a solvent mixture of terpineol and methanol, ethyl cellulose and CGO powder. Successful printing of regular drops was achieved after printing optimisation. It has been demonstrated that inkjet printing is a promising technique for high quality membrane fabrication for applications including solid oxide fuel cells. The ink formulation and optimisation procedure would also be applicable for other ceramic ink development.
    Journal of the European Ceramic Society 08/2012; 32(10):2317–2324. DOI:10.1016/j.jeurceramsoc.2012.03.001 · 2.95 Impact Factor
  • E.villa · A.tuissi · R.tomov · J. E.evetts
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    ABSTRACT: For the production of HTS coated conductor devices, NiV and NiCr (Ni-based alloys) are the most important, non-magnetic, high strength and biaxially textured substrates developed from pure Ni. The Ni88V12 and Ni85Cr15 (at. %) alloys have been melted in Plasma Arc Furnace and textured tapes have been prepared, after heavy cold rolling, by recrystallization heat treatment under high vacuum. The suitable working conditions have been found to obtain not only the {100} <001> cube texture but also the correct grain shape and size for the following deposition process. Out of plane orientation of these substrates has been investigated by θ-2θ X-ray diffraction measurements and in plane orientation study has been completed by pole figures. The microstructure has been observed by optical microscopy: it has been carried out on samples obtained after an annealing treatment (Grain Size Adjustment) and on recrystallized samples in different conditions. As preliminary mechanical investigation the microhardness values have been detected for each step of the working procedure. The accuracy of the cubic texture and the grain structure are affected by the processing condition, in particular the temperature of the GSA seems a very important parameter which influences the final characteristics of the tapes.
    International Journal of Modern Physics B 01/2012; 14(25n27). DOI:10.1142/S0217979200003459 · 0.94 Impact Factor
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    ABSTRACT: A sol–gel-based precursor solution of gadolinium-doped ceria (CGO) was developed for deposition by inkjet printing. A stable precursor was synthesised by dissolving stoichiometric amounts of cerium (III) acetate hydrate and gadolinium (III) acetate hydrate in propionic acid, and diluted to 0.75M with 1-propanol. The sintering behaviour of the printed precursor was investigated. Since the commonly used method of dilatometry is only applicable to bulk samples, an alternative approach using Differential scanning calorimetry (DSC) has been explored. The sintering temperature of the printed precursor was estimated by subtracting contributions from energy stored due to heat capacity and activation energy of ionic mobility from the DSC heat flow signal. Based on this modelling it was found that the optimum sintering temperature of the acetate-based CGO precursor was 1100±55°C, a result independently confirmed by SEM imaging of printed precursor coating on NiO-YSZ cermet. A gadolinium-doped ceria (CGO) thin film was then directly deposited on a porous NiO-YSZ cermet anode composite by inkjet printing. After co-sintering, it was shown that crack-free and continuous coating thinner than 10μm of CGO can be readily produced. These results suggest that the inkjet printing technique can be successfully implemented to fabricate a thin film of dense electrolyte (>98%) for solid oxide fuel cell (SOFC) applications.
    Journal of Materials Science 11/2011; 46(21):6889-6896. DOI:10.1007/s10853-011-5653-y · 2.37 Impact Factor
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    ABSTRACT: Electromagnetic drop-on-demand direct ceramic inkjet printing (EM/DCIJP) was employed to fabricate dense yttria-stabilized zirconia (YSZ) electrolyte layers on a porous NiO–YSZ anode support from ceramic suspensions. Printing parameters including pressure, nozzle opening time and droplet overlapping were studied in order to optimize the surface quality of the YSZ coating. It was found that moderate overlapping and multiple coatings produce the desired membrane quality. A single fuel cell with a NiO–YSZ/YSZ (∼6 μm)/LSM + YSZ/LSM architecture was successfully prepared. The cell was tested using humidified hydrogen as the fuel and ambient air as the oxidant. The cell provided a power density of 170 mW cm−2 at 800 °C. Scanning electron microscopy (SEM) revealed a highly coherent dense YSZ electrolyte layer with no open porosity. These results suggest that the EM/DCIJP inkjet printing technique can be successfully implemented to fabricate electrolyte coatings for SOFC thinner than 10 μm and comparable in quality to those fabricated by more conventional ceramic processing methods.
    Journal of Power Sources 11/2010; 195(21):7160-7167. DOI:10.1016/j.jpowsour.2010.05.044 · 6.22 Impact Factor
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    ABSTRACT: The successful inkjet printing of a cerium gadolinium oxide (Ce0.8Gd0.2O2) precursor solution on highly textured Ni-5%W is reported. A stable ink was synthesised from metal acetates and propionic acid with rheological properties suitable for inkjet printing and also the development of solid–liquid interface comparable with thin film formation by dip coating. Two different drop-on-demand print heads were used for deposition: a 16-nozzle piezoelectric cartridge and a single electromagnetic nozzle. Two different rastering patterns with different droplet sizes and spacing were compared. Thermogravimetry and X-ray diffractometry were used to study the thermal decomposition of the metal oxide precursors and to determine the shortest possible heat treatment of the deposited layers, potentially suitable for continuous large scale production. The results from X-ray diffraction show that the single phase Ce0.8Gd0.2O2 was obtained in all cases, but only piezoelectric inkjet printing with optimised drop overlapping produces a highly textured buffer layer. Optical micrographs and atomic force microscopy also indicate the good quality of deposited films after heat treatment. KeywordsInkjet printing-Sol–gel-Ce0.8Gd0.2O2 -Thin films
    Journal of Sol-Gel Science and Technology 05/2010; 54(2):154-164. DOI:10.1007/s10971-010-2170-4 · 1.55 Impact Factor
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    ABSTRACT: The successful inkjet printing of multiple cerium gadolinium oxide (Ce0.8Gd0.2O2) layers on highly textured Ni-5%W is reported using a stable ink, developing a solid-liquid interface comparable with that arising from dip coating. Two different approaches were used for the deposition of CGO layers using a 16-nozzle piezoelectric drop-on-demand print head. Two overlapping square arrays of droplets with constant volume and spacing were printed, with and without an intermediate CGO crystallization. The shortest possible heat treatment of the deposited layers was applied, potentially suitable for continuous large scale production. The results from X-ray diffraction show that the single phase Ce0.8Gd0.2O2 was obtained in all cases, but only the approach with intermediate CGO crystallization can produce a highly textured buffer layer. Optical micrographs and atomic force microscopy (AFM) also indicate the good quality of deposited films after heat treatment.
    Journal of Physics Conference Series 01/2010; 234(2). DOI:10.1088/1742-6596/234/2/022024
  • Rumen I. Tomov · Mark Blamire
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    ABSTRACT: Systematic study of pulsed laser deposition of non-c-axis-oriented polycrystalline SrBi2Ta2O9 ferroelectric thin films oil Pt-coated silicon substrates has been performed. Both ill situ and ex situ routes have been explored. Ex situ deposited filius produced predominantly (115) and (200) orientations, While in situ deposition resulted in a Mixture of (115) and (104) orientations. The growth was Studied as a function of the ceramic targets Bi-enrichment, target-substrate distance, annealing temperature, and the utilization of an external electric field applied oil the Substrate during the post-annealing procedure. Variation of those parameters appears to significantly affect the phase purity and crystalline quality of the films. The minimization of pyrochlore and fluorite phases and the related Bi2Pt formation have been achieved through the introduction of layered Bi-enrichment gradient architecture and lowering the annealing temperature. SBT d(33) piezoelectric coefficients of an order of 12- 15 were measured. X-ray diffraction was used to characterize structural perfection of the Films. The nanoscale mechanism of piezoelectric behavior has been investigated by means of piezoresponse force microscopy.
    Plasma Processes and Polymers 02/2006; 3(2):241 - 247. DOI:10.1002/ppap.200500119 · 2.96 Impact Factor
  • B.S.H. Pang · C. Bell · R.I. Tomov · J.H. Durrell · M.G. Blamire
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    ABSTRACT: La0.7Ca0.3MnO3/YBa2Cu3O7−δ/La0.67Sr0.33MnO3 heterostructural devices with double coercivity have been fabricated. The superconducting critical current (Ic) and critical temperature in both parallel (P) and antiparallel (AP) magnetic configurations remained unchanged within our measurement limits. This observation is contrary to results obtained elsewhere using similar metallic systems. A pseudo spin-valve magnetoresistive (MR) characteristic was observed at bias current (Ibias)∼Ic at temperatures below the onset of superconductivity. The effect increased with decreasing temperature and Ibias and can be explained using the assumption of the electron spin-charge separation.
    Physics Letters A 06/2005; 341(1-4-341):313-319. DOI:10.1016/j.physleta.2005.04.072 · 1.63 Impact Factor
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    ABSTRACT: Transport properties of aliovalent-ion-doped BiFeO3 (BFO) thin films have been studied in order to identify the cause of high leakage currents. Doping of 2 at. % Ti4+ ions increased the dc resistivity by more than three orders of magnitude. In contrast, doping of 2+ ions such as Ni2+ reduced the dc resistivity by two orders of magnitude. Current–voltage (I–V) characteristics indicated that the main conduction mechanism for pure and Ni2+ doped BFO was space charge limited, which was associated with the free-carriers trapped by the oxygen vacancies, whereas in the Ti4+ doped BFO, field-assisted ionic conduction was dominant.
    Applied Physics Letters 01/2005; 86(6):062903-062903-3. DOI:10.1063/1.1862336 · 3.52 Impact Factor
  • B. S. H. Pang · R. I. Tomov · C. Bell · M. G. Blamire
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    ABSTRACT: In this investigation, we deposited multilayers of [(La0.67Sr0.33MnO3)d/(YBa2Cu3Oy)x], [(La0.7Ca0.3MnO3)4/(YBa2Cu3O7)x]180nm and [(La0.45Ca0.55MnO3 )4/(YBa2Cu3O7)x]180nm of varying individual layer thicknesses using the ‘eclipse’ pulsed laser deposition technique. Transport measurements were performed to obtain the films’ critical temperatures (Tc). We study the interaction between superconductivity and magnetism within these heterostructures, paying attention to the superconducting and ferromagnetic coherence lengths, ξF and ξS respectively, of the materials in the system, and analyzing how these parameters affect the suppression of Tc, eliminating stray field as a possible cause of Tc suppression. We compared our data to previous work to achieve a more comprehensive study of oxide F/S multilayers. We observe that the magnetic nature of the manganite layers do not have much influence on Tc suppression in the multilayers. We show that within certain limits, the thicknesses of both the superconducting and ferromagnetic layers individually affect the Tc of the multilayers. The critical thickness of YBCO in our multilayers was estimated to be ∼20nm.
    Physica C Superconductivity 10/2004; 415(3):118-124. DOI:10.1016/j.physc.2004.08.005 · 1.11 Impact Factor